Celiac Sprue is a hereditary digestive disease in which dietary exposure to gluten from sources such as wheat, rye and barley induces an inflammatory response, leading to destruction of the villous structure of the small intestine. Despite its high prevalence (>1:200) and serious clinical manifestations, the molecular basis of this autoimmune disorder is unclear. There is no therapeutic option available to Celiac Sprue patients, and the only "treatment" of this disease is lifelong adherence to a strict gluten-flee diet. Our long-term goals are to understand the biochemical basis of Celiac Sprue, and to translate these insights into pharmacological agents that could allow patients to safely re-incorporate these otherwise nutritious and extremely common foodgrains into their diet. Recently, several Pro- and Gin-rich epitopes have been identified from primary sequences of gluten proteins that are exclusively recognized by gut-derived T cells from Celiac patients but not controls. The most potent of these epitopes have three remarkable properties. First, they are unusually resistant to proteolysis by gastric, pancreatic and intestinal brush border enzymes. Second, they are high-affinity substrates of tissue transglutaminase (TG2), the predominant auto-antigen associated with this autoimmune disorder. Third, the deamidated products of the TG2 catalyzed reaction are high-affinity ligands for HLA-DQ2, a class II major histocompatibility complex present in >90% of Celiac Sprue patients. A working model has emerged for the pathogenesis of Celiac Sprue. According to this model, intestinal villous damage is primarily induced when dietary gluten is recognized by inflammatory (CD4+) T-helper cells in a TG2-dependent and DQ2-dependent manner. To the extent this is a valid model, it may be possible to develop a therapeutic alternative to a gluten-free diet by either (i) supplementing the Celiac diet with an exogenous prolyl endopeptidase capable of hydrolyzing proteolytically resistant immunogenic gluten epitopes, or (ii) local inhibition of TG2 in small intestinal tissue, or (iii) inhibiting HLA-DQ2 mediated presentation of gluten to disease-specific T cells. We propose to conduct biochemical studies to understand the mechanisms by which dietary gluten triggers an immunotoxic response in the small intestine of a Celiac patient. The following Specific Aims are proposed: 1) Identification of physiologically relevant immunogenic gluten peptides; 2) Fundamental studies on the feasibility of using prolyl endopeptidases to counter the toxic effects of gluten; and 3) Elucidating the role of tissue transglutaminase in the inflammatory response to gluten. In addition to shedding light on the earliest molecular events in the complex cascade that leads to gluten-induced enteropathy, these studies will provide a fundamental basis for developing a therapeutic approach to Celiac Sprue.